This application relates to the placement of a heat exchanger in a gas turbine engine bypass duct where a fan is controlled to selectively draw air across the heat exchanger.
Gas turbine engines are known and typically include a fan delivering air into a bypass duct as propulsion air and into a compressor as core airflow. The air is compressed in the compressor and delivered into a combustion section where it is mixed with fuel and ignited. Products of this combustion pass downstream over turbine rotors, driving them to rotate.
As known, there are a number of accessories associated with a gas turbine engine. Various fluids associated with the accessories require cooling. Thus, it is known to place heat exchangers into various locations in a gas turbine engine.
One such location is in the bypass duct, such that a fluid within the heat exchanger is cooled by the bypass air. However, the pressure ratio delivered by the fan is becoming lower with the recent advent of a gear reduction driving the fan rotor at slower speeds. In addition, during the course of operation of a gas turbine engine associated with an aircraft, the amount of air driven through the bypass duct will vary. Further, the cooling challenges on the heat exchanger will vary. As an example, at takeoff conditions, the cooling load will tend to be greater than it will be at cruise conditions.
Known gas turbine engines have heat exchanger which are sized for the highest heat load challenge.